This invention relates to a composite material comprising nanoporous particles, more particularly an aerogel composite material, a process and a composition for producing the composite material, and also the use of the composite material.
Aerogels and aerosils are highly porous solid bodies in that the predominant portion of their volume consists of pores. Aerogels can be based for example on silicate but also on plastics or carbon. The diameter of aerogel pores is in the nanometer range. Owing to their high pore volume, aerogels are particularly useful as insulating materials combining outstanding insulation properties with low density. Aerogels are initially present as particles, and can be subjected with the use of binders to a shaping process to form plates by pressing for example.
Aerogels are also described in the literature as gels with air as dispersion medium. Aerogels are obtainable by drying a suitable gel. Aerogel in the context of the present invention also comprehends xerogels and cryogels. The shaping process of the aerogel is concluded during the sol-gel transition. Once the solid gel structure has become developed, the outer form can only be changed by comminution, for example grinding.
EP-A-0 340 707 discloses insulating materials from 0.1 to 0.4 g/cm3 in density with good thermal insulation capacity and sufficiently high compressive strength, which are obtained by adhering silica aerogel particles together using an organic or inorganic binder. Cement, gypsum, lime or waterglass are mentioned as examples of suitable inorganic binders.
EP 489 319 A2 discloses composite foams based on silica aerogel particles and a styrene polymer foam. U.S. Pat. No. 6,121,336 discloses improving the properties of polyurethane foams by incorporation of silica aerogels. DE 44 41 567 A1 discloses composite materials from aerogels and inorganic binders where the aerogel particles have corpuscle diameters of less than 0.5 mm. EP 672 635 A1 discloses shaped articles from silica aerogels and binders that additionally utilize sheet-silicates or clay minerals. U.S. Pat. No. 6,143,400 discloses composite materials from aerogel particles and an adhesive that utilize aerogel particles having diameters less than 0.5 mm. DE 105 335 64 A1 discloses composite materials comprising aerogel particles, binders and a fiber agent. WO 2007/011988 A2 discloses compositions with so-called hybrid aerogel particles and a binder wherein the aerogel particles may form covalent bonds with the binder.
However, producing shaped articles of this type frequently necessitates the use of high binder contents. In addition, many performance characteristics such as, for example, thermal conductivity or breaking strength are still in need of improvement. There are frequently also issues with the production of shaped articles. Numerous organic binders cannot be used on account of their high viscosity. The use of low-viscosity dispersions frequently requires an excessive degree of dilution with aqueous solvents, which has the disadvantage that the binder in the dispersions does not enter any bond with the generally hydrophobic silica aerogel particles owing to the absence of aerogel surface wetting.